Stabilizing selection
occurs when phenotypes at both extremes of the phenotypic distribution are selected against. This narrows the range of variation. An example is human birth weight. Babies that are very large or very small at birth are less likely to survive.
What type of natural selection is most likely at work regarding the birth weight of babies?
Birth weight is a classic example of a trait under
strong stabilizing selection
, where high and low birth weights are correlated with reduced survival in both males and females (22).
What kind of selection is likely to happen in human birth weight?
Birth weight is a classic example of a trait under
strong stabilizing selection
, where high and low birth weights are correlated with reduced survival in both males and females (22).
What is directional selection?
Directional selection occurs
when individuals with traits on one side of the mean in their population survive better or reproduce more than those on the other
. It has been demonstrated many times in natural populations, using both observational and experimental approaches.
What causes stabilizing selection?
Simply stated, there is no common cause of stabilizing selection, besides the fact that the most average individual is selected for. In that way, like all forms of selection, the cause of stabilizing selection is
the increased fitness and reproductive success that the median individuals have
.
Which type of selection is the most likely to result in speciation?
Diversifying (or disruptive) selection
: Diversifying selection occurs when extreme values for a trait are favored over the intermediate values. This type of selection often drives speciation. Diversifying selection can also occur when environmental changes favor individuals on either end of the phenotypic spectrum.
What is natural selection examples?
Natural selection is the process in nature by which organisms better adapted to their environment tend to survive and reproduce more than those less adapted to their environment. For example,
treefrogs are sometimes eaten by snakes and birds
. … This explains the distribution of Gray and Green Treefrogs.
What types of selection are there?
- stabilizing selection.
- directional selection.
- diversifying selection.
- frequency-dependent selection.
- sexual selection.
Is directional selection the most common?
Evidence. Directional selection occurs most
often under environmental changes
and when populations migrate to new areas with different environmental pressures. Directional selection allows for fast changes in allele frequency, and plays a major role in speciation.
What’s an example of disruptive selection?
Disruptive Selection Examples: Color
Light-colored oysters would blend into the rocks in the shallows
, and the darkest would blend better into the shadows. The ones in the intermediate range would show up against either backdrop, offering those oysters no advantage and make them easier prey.
What is directional selection for kids?
A directional selection is
a force in nature that causes a population to evolve towards one end of a trait spectrum
. … Directional selection can also be compared to disruptive selection, or a selection that causes an increase in both extremes of a trait spectrum.
What type of selection is Darwin’s finches?
Pioneer evolutionary scientist Charles Darwin (1809–1882) studied what later became known as
directional selection
while he was in the Galapagos Islands. He observed that the beak length of the Galapagos finches changed over time due to available food sources.
What are the 3 types of selection?
- Stabilizing Selection.
- Directional Selection.
- Disruptive Selection.
Which type of selection is most common?
The most common of the types of natural selection is
stabilizing selection
. In stabilizing selection, the median phenotype is the one selected for during natural selection.
Which type of selection is most likely to take place in environments that don’t change?
This is thought to be the most common mechanism of action for natural selection because most traits do not appear to change drastically over time.
Stabilizing selection
commonly uses negative selection (a.k.a. purifying selection) to select against extreme values of the character.
Which type of selection is most likely to create two distinct phenotypes?
Disruptive selection
occurs when individuals at the upper and lower ends of the curve have higher fitness than individuals near the middle. Disruptive selection acts against individuals of an intermediate type and can create two distinct phenotypes.
Which of the following will most likely decrease genetic diversity?
Inbreeding, genetic drift, restricted gene flow, and small population size
all contribute to a reduction in genetic diversity. Fragmented and threatened populations are typically exposed to these conditions, which is likely to increase their risk of extinction (Saccheri et al.
Which best describes natural selection?
Natural selection is the process through
which populations of living organisms adapt and change
. … Over time, these advantageous traits become more common in the population. Through this process of natural selection, favorable traits are transmitted through generations.
Which type of natural selection occurs when an intermediate phenotype is favored?
Stabilizing selection
When individuals with intermediate phenotypes are favoured and extreme phenotypes are selected against, the selection is said to be stabilizing.
Which type of selection maintains stable frequencies?
For example, if heterozygotes at a locus have higher fitness than homozygotes (a scenario known as heterozygote advantage or overdominance),
natural selection
will maintain multiple alleles at stable equilibrium frequencies.
What is the best example of natural selection quizlet?
Which is the best example of natural selection? –
Some insects in a population survive temperature changes and pass their traits on to their offspring
.
Is the best example of natural selection?
Tree frogs
are the best examples of natural selection.
Natural selection is a natural process in which organisms that are more adapted to their environment successfully reproduce more than those that are not. Snakes and birds, for example, have been known to devour tree frogs.
Which type of selection is most common quizlet?
Directional selection
is the most common pattern of natural selection, in which individuals at one extreme of an inherited phenotypic trait have an advantage over other individuals in the population.
What are the three types of selection give an example of each one?
Directional selection, stabilizing selection and disruptive selection
are three types of natural selection. They are also examples of adaptive evolution. Natural selection is the mechanism of evolution which favors organisms that are better adapted to their environments.
What are the different types of selection pressures?
- Resource availability – Presence of sufficient food, habitat (shelter / territory) and mates.
- Environmental conditions – Temperature, weather conditions or geographical access.
- Biological factors – Predators and pathogens (diseases)
Is human birth weight directional selection?
There are several classic examples in animals and humans of the results of stabilizing selection process: Human birth weight, especially in underdeveloped countries and in the past of the developed world, is a
polygenetic selection
which is controlled by environmental factors.
What is descriptive selection give example?
e.g. Disruptive selection was
observed in the different beak sizes of African seed cracker finches
. The birds have different sizes of the beak and they feed on seeds. The available seeds were of two kinds i.e., small and large-sized seeds.
What is an example of balancing selection?
A well-studied case is that of
sickle cell anemia in humans
, a hereditary disease that damages red blood cells. … This is an example of balancing selection between the fierce selection against homozygous sickle-cell sufferers, and the selection against the standard HgbA homozygotes by malaria.
What are the 3 types of natural selection quizlet?
- Stabilizing Selection. average form of a trait is favored.
- Directional Selection. one extreme form of a trait is favored.
- Diversifying Selection. both extremes of a trait are favored over an average form of a trait.
How is birth weight stabilizing selection?
Stabilizing Selection in Humans. Karn & Penrose (1951) showed that
birth weight follows a normal distribution
, that mortality for newborns is greater for those either under- or over-weight, and that the mean birth weight (7 lbs) coincides with that showing minimum mortality.
What do directional selection and disruptive selection have in common?
Similarities Between Directional and Disruptive Selection
Both
increase the allele frequency of the favored phenotypes within the population
. However, they may increase or decrease biological phenotypes within a population. The decrease in the number of phenotypes within a population reduces variation.
What are the 3 components of natural selection?
The essence of Darwin’s theory is that natural selection will occur if three conditions are met. These conditions, highlighted in bold above, are a struggle for
existence, variation and inheritance
. These are said to be the necessary and sufficient conditions for natural selection to occur.
What are the 3 principles of natural selection?
Natural selection is an inevitable outcome of three principles:
most characteristics are inherited, more offspring are produced than are able to survive, and offspring with more favorable characteristics will survive and have more offspring than those individuals with
less favorable traits.
What is directional selection quizlet?
1:Directional Selection occurs
when selection favors one extreme trait value over the other extreme
. This typically results in a change in the mean value of the trait under selection. … 3:Stabilizing Selection occurs when selection favors the intermediate trait value over the extreme values.
What leads to directional selection?
Directional selection occurs when
individuals homozygous for one allele have a fitness greater than that of individuals with other genotypes
and individuals homozygous for the other allele have a fitness less than that of individuals with other genotypes.
How does a directional selection graph work?
When directional selection occurs, phenotypes at
one end of the spectrum are selected against
, and phenotypes at the other end of the spectrum are selected for. … The bottom graph shows what happens after directional selection.
What type of selection did the finch population experience?
A long-term study of finch populations on the island of Daphne Major has revealed that evolution occurs by
natural selection
when the finches’ food supply changes during droughts.
What is the selective pressure in the evolution of Darwin’s finches?
The relative proportion of these seeds varies from year to year, and thus exerts a
strong selective pressure
on these finches, particularly in drought years and El Niño years; the beak size and strength is determined by only a handful of genes and so is quite susceptible to evolutionary forces.
How are Darwin’s finches an example of natural selection?
However, the Galapagos finches helped Darwin solidify his idea of natural selection. The favorable adaptations of Darwin’s Finches
‘ beaks were selected for over generations until they all branched out to make new species
. These birds, although nearly identical in all other ways to mainland finches, had different beaks.
